The present invention relates to a semiconductor device used for a light emitting diode (LED) array and the likes; a light emitting diode (LED) print head including the semiconductor device; and an image forming apparatus including the light emitting diode (LED) head. In the semiconductor device, a plurality of light emitting elements is formed of a thin layer formed of a compound semiconductor, and is arranged in one direction with an equal interval therebetween.
In a conventional image forming apparatus such as a printer using electro-photography technology, a plurality of light emitting diodes (LEDs) is arranged in a row to form an LED array chip, and a plurality of the LED array chips is arranged in a row to form an optical head (exposure head or LED print head). Recently, it has been required that an image forming apparatus such as a printer forms an image with high resolution. Accordingly, the number of the light emitting elements in the LED print head has increased drastically.
In the LED print head, a drive circuit of a light emitting diode may be formed in a substrate formed of silicon in advance. In a separate step, an LED array (LED array film) is formed in a thin layer formed of a compound semiconductor formed through an epitaxial growth process, so that the drive circuit is connected to the LED array film (refer to patent Reference).
Patent Reference: Japanese Patent Publication No. 2004-179641
In the LED print head described above, a plurality of LEDs is formed in the LED array film. Each of the LEDs includes an ohmic electrode on a front surface of the LED array film for contacting (ohmic contact or resistor type contact) with one of a p-type conductive side and an n-type conductive side. Another ohmic electrode is formed on a backside of the LED array film (facing the substrate with the drive circuit formed therein) for contacting the other of the p-type conductive side and the n-type conductive side. In the configuration, the ohmic electrodes formed on the backside of the LED array film are commonly connected to the LEDs arranged next to with each other, so that the LEDs concurrently emit light.
Alternatively, it may be configured that not all of the LEDs may emit light, thereby reducing heat and power consumption. In this case, the ohmic electrodes of both of the n-type conducive side and the p-type conductive side are disposed on the front surface of the LED array thin layer chip.
When the LED array chip is formed of the thin layer (LED array film), as opposed to the case that the LED array is directly formed on the substrate formed of a compound semiconductor, the LED array film has a relatively low strength. Accordingly, when the ohmic electrodes of both of the n-type conducive side and the p-type conductive side are disposed on the front surface (same surface) of the LED array thin layer chip, the ohmic electrodes tend to crack.
In particular, when the ohmic electrodes extend in a longitudinal direction of the LED array thin layer chip, the ohmic electrodes become susceptible to crack during a manufacturing process of connecting the ohmic electrodes to the drive circuits, or upon receiving a stress or a temperature change.
In view of the problems described above, an object of the present invention is to provide a semiconductor device with improved reliability, in which a semiconductor thin layer is provided with an electrode and a contact portion with high reliability even when ohmic electrodes of both of an n-type conducive side and a p-type conductive side are disposed on a same surface of an LED array thin layer chip and the ohmic electrodes partially crack.
Further objects and advantages of the invention will be apparent from the following description of the invention.